The present invention relates generally to communication systems, and more particularly, to an improved system and method for transporting asynchronous transfer mode (ATM) information over a communications channel such as a digital subscriber line (DSL).
Data communication typically occurs as the transfer of information from one communication device to another. This is typically accomplished by the use of a modem located at each communication endpoint. In the past, the term modem denoted a piece of communication apparatus that performed a modulation and demodulation function, hence the term xe2x80x9cmodemxe2x80x9d. Today, the term modem is typically used to denote any piece of communication apparatus that enables the transfer of data and voice information from one location to another. For example, modem communication systems use many different technologies to perform the transfer of information from one location to another. Digital subscriber line (DSL) technology is one vehicle for such transfer of information. DSL technology uses the widely available subscriber loop, the copper wire pair that extends from a telephone company central office to a residential location, over which communication services may be provisioned. DSL devices can be referred to as modems, or, more accurately, transceivers, which connect the telephone company central office to the user, or remote location typically referred to as the customer premises. The transport of communication over a DSL communication channel generally consists of a physical layer modulation over which asynchronous transfer mode (ATM) communication occurs. ATM is typically achieved through the transport of packets of information referred to as xe2x80x9ccellsxe2x80x9d. An ATM cell is 53 octets in length, an octet consisting of one byte of information. DSL technology encompasses many varieties of modulation techniques over the subscriber loop including, but not limited to, carrierless amplitude modulation (CAP), quadrature amplitude modulation (QAM) and variations thereof, etc.
ATM offers the advantages of a connection based architecture and efficient processing in the core network switches. The core network switches are those devices that comprise the network over which a plurality of telephone company central offices may communicate. This network is sometimes referred to as a xe2x80x9cbackendxe2x80x9d network.
The small, fixed size of an ATM cell can also provide low latency for real-time data transfer. ATM cells however, also require additional processing at an endpoint, or remote, transceiver device, thus giving rise to additional cost and complexity required at a remote device. Furthermore, ATM cells require a large amount of overhead, thus reducing the user data throughput over the DSL communication channel. In the past, ATM cells were communicated over a DSL communication channel, thus tolerating the excessive overhead for the ability to transport ATM over the DSL communication channel and, in turn, over the backend network.
One possible solution to the problem of transporting ATM over a DSL communication channel was developed in the form of framed user network interface (FUNI). FUNI created frames within which ATM information may be transported over a DSL communication channel. FUNI has a number of disadvantages however. For example, the communication header associated with FUNI differs significantly from the standard five octet ATM cell header. Significant processing resources are expended in converting the FUNI header to an ATM cell. Also, FUNI may only transport AAL5 (ATM adaptation layer 5) frames. There is no other method to transport other AAL types. The basic purpose of the AAL layers is to isolate the higher communication layers from the specific characteristics of the ATM layer by mapping the higher layer protocol data units (PDU""s) into the information field of the ATM cell and vice versa.
Furthermore, FUNI does not allow the transport of real-time applications, such as telephone communication, and FUNI does not allow support for ABR (available bit rate) data because FUNI fails to provide for RM (resource management) cells, which are indicated by a special bit combination in the PTI (payload type indicator) of the cell header.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies in the transport of ATM information over a DSL communication channel.
The present invention provides an improved system and method for communicating over a digital subscriber line.
The system of the present invention uses a novel header application which enables the transport of ATM data efficiently and economically over a communications channel, such as a DSL communications channel.
Briefly described, in architecture, the system can be implemented as follows. An improved system for communicating over a digital subscriber line, comprises means for forming a data frame, the data frame comprising a header; a trailer, a first frame delimiter and a second frame delimiter, the frame delimiters encompassing a plurality of fields, and means for forming a payload, the payload comprising the first four octets of a five octet Asynchronous Transfer Mode (ATM) header combined with user data. Alternatively, the payload may comprise at least one 52 octet ATM cell. The header also includes means for indicating whether the payload comprises the first four octets of a five octet Asynchronous Transfer Mode (ATM) header combined with user data, or whether the payload comprises the 52 octet ATM cells.
The present invention can also be viewed as providing an improved method for communicating information over a digital subscriber line. In this regard, the method can be broadly summarized by the following steps: forming a data frame, the data frame comprising a header, a trailer, a first frame delimiter and a second frame delimiter, the frame delimiters encompassing a plurality of fields, and forming a payload, the payload comprising the first four octets of a five octet Asynchronous Transfer Mode (ATM) header combined with user data. Alternatively, the payload may comprise at least one 52 octet ATM cell. The method also includes the step of determining whether the payload comprises the first four octets of a five octet Asynchronous Transfer Mode (ATM) header combined with user data, or whether the payload comprises the 52 octet ATM cells.
The present invention has numerous advantages, a few of which are delineated hereafter as merely examples.
An advantage of the invention is that the overhead of a communication channel is reduced, thus allowing higher throughputs of data.
Another advantage of the invention is that a number of processing tasks are moved to a central communications device. This results in reduced cost as compared to performing these processing tasks in the remote communications device.
Another advantage of the invention is that it supports the communication of all ATM adaptation layer (AAL) information.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention.